Thoriated tungsten filament



Patentedilune 17, 1930 v} UNITED STATES PATENT orl-"lcs JOHN HUMPHREYS IRA-IMAGE, F I BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA THORIATED TUNGSTEN FILAMEN'J.

Application filed m 27,

This invention relates to electric incandescent lamps and more particularly to a method of improving the oifset-resisting properties of a filament such as a tungsten filament.

In vacuum type lamps it has been customary to employ as the incandescent body a tungsten filament containing an offset-resisting material such as thorium oxide. It

has been found that filaments of this character are at times subject to an early burn-out, that is, lamps embodying thoriated tungsten filaments sometimes fail before the lamp has burned a useful period of time. In investigating this matter I have found that the cause for early burn-outs may be'primarily occasioned by the lack of uniform distribution of the thorium-oxide throughout the filament and the fineness of division of the thoria 2o particles.

' I have discovered that a thoriated tungsten filament may have a longer life when the added or auxiliary thoriated material is in a fine state of subdivision and is uniformly dis- 26 tributed throughout the filament.

Therefore, it is an object of my invention to provide a method whereby the thoria con- -tent of a thoriated tungsten filament is in a fine state of subdivision and uniformly dis- 80 tributed throu hout the filament.

A further bject of my invention is to provide a method of increasing the burn-out .life of a thoriated tungsten filament.

' A still further object of my invention is to as improve the qualities of a thoriated tungsten filament so as to increase its burn-out life.

Other objects of the invention will become apparent'as the following detailed description is read.

4 Briefly stated, the invention consists in thoroughly disseminating throughout a tungsten filament, thoria particles of extremel vsmall size; This may be accomlishe ,in one or more ways, such as by orming solutions containing the constituent ingredients and simultaneously precipitating-the materials therefrom. It is to be appreciated that in practicing my invention such factors as the dilution of the'thoriating I0 matcrip-l','temperature of the solution during 1926. Serial 170. 125,833.

for each case as the foregoing factors must be altered to suit specific conditions.

Fig. 1 is a diagram or flow sheet indicating the various steps employed in the preparatemtion of the intimate. mixture of tungsten and thorium oxide; and,

Fig. 2 is a diagram offiow sheet of the various steps employed in'the preparation of an intimate mixtureof tungsten, thorium oxide and carbon.

One embodiment of my invention consists in simultaneously precipitating tungstic oxide (W0 and the doping reagent, which latter for the sake of convenience, will be con-. sidered as thorium oxide. Since tungstie oxide is acid and thorium'oxide basic, this cannot be done directly by precipitation together from a mixed solution of solvents.

However, I have found that the desired result may be accomplished by the followingprocedure.

I first form a. solution consisting of 750 grams of tungstic oxide, 706 cc. of ammonia (28%) 1765 cc. of water and-2.7 grams of ammonium fluoridev (dehydrated). I next form a solution of 508 cc. HCl (36%) and 1 12.5 grams of Th(NO5) 12 H O. The first solution is heated and while hot is pouredinto the second solution. This results in a precipitate consisting of tungsticoxide and thorium fluoride. The precipitate is removed, washed and dried and then reduced by passing hydrogenthereover. The hydrogen reduction is effectedrin a mannersimilar to that at present practiced in the reduc: tion of tungstic oxide to metal. The results" ant product thus obtained will be found to consistof an intimate mixture of tungsten and thorium oxide, the latter being in a fine uted through the tungsten.

state of subdivision and uniformly distribc The reaction is as renews: ThF,+WO dry H2= Although a small amount of tungsten is lost through the removal of the fluorine, the

amount-thereof can be readily calculated and adequate provision made therefor in preparmg the solutions.

In preparing filaments for radio tubes it is desirable to introduce carbon into the ployed for vacuum lamps.

thoria-doped tungsten. Wire of this nature although especially suitable for producing an .actlvated tungsten filament may be em- In preparing a filament of this character the following procedure may be followed.

A solution is prepared consisting of 750 grams of tungstic oxide (W0 706 cc. of

V ammonia '(NILOH) (29%), 1765 cc. of

water and 5.15 grams of ammonia oxalate ((NH C O .H O). Av second solution is also prepared consisting of 508 cc. of hydrochloric acid (H01) (36%) and 12.5 grams thorium nitrate (Th(NO )4.H O). The precipitate is obtained hot by pouring the first'solution into the second and consists of W0, and Th (C 00 The precipitate is washed and dried and then reduced by dry hydro en at a low temperature short reducr ing so edule. The reaction is as follows:

W03 (C20 2 +11 1 v The powder thus obtained may be agglomerated, sintered and heat treated to produce a slug or bar of dense coherent metal after which it may be worked down in accordance with standard practice to filamentary sizes. The filament thus obtained may be mounted in a radio tube and subsequently 7, heat treated by well known methods to bring about a reduction of the thorium oxide to thorium to obtain the activation of the filament. v

Modifications of the invention may'o ccur to those skilled in the art but such modifications are contemplated by me as come within the scope of the invention as defined by the appended claims. I What is claimed is: i 1. The method of preparing thoriated tungsten which comprises simultaneously effecting the precipitation of tungstic acid ducing the tungsten contentof the precipitate to metal with ydrogen.

tungsten metal powder which comprises separately forming an alkaline solution of a tungsten compound and an acid solution of a thorium compound, adding to said alkaline solution a proportion of a soluble compound capable of reaction with the thorium content of the said acid solution to form acid insoluble compounds of thorium, admixing the two solutions while one of the'solutions is heated, rendering the admixed solutions acid to effect the precipitation of the acid insoluble thorium compound and the tungsten content of the solutions, separating the'precipitated thorium and tungsten compounds from the solution, and thereafter subjecting the precipitate to the action of a reducingagent. i

- 4. The method of preparing thoriated tungsten metal powder which comprises forming an alkaline solution I of tungsten oxide, forming an acid solution of a thorium compound, adding to the alkaline solution a proportion of a compound reactive with the thorium content of the acid solution to form an acid insoluble. compound, admixing the two solutions, acidifying the admixed solution to eifecta precipitation of the insoluble thorium and tungsten compounds, recovering the precipitate and thereafter effecting the reduction ofthe tungsten content of the precipitate to metal in any suitable manner.

5. The method of preparing thoriated tungsten metal powder which comprises forming an ammoniacal solution of tungsten trioxide, forming an acid solution of thorium nitrate, adding to the tungsten solution a proportion of ammonium fluoride suflicient in amount to react with the entire thorium content of the thorium nitrate solution, admixing the two solutions, acidifying the admixture to effect the separation of tungstic acid, recovering the precipitate, and eflecting a reduction of thetungsten content to metal in any convenient manner.

6. The method of preparing thoriated tungsten metal powder which comprises forming an ammoniacal solution of tungsten trioxide, adding thereto a proportion of ammonium fluoride, acidifying the solution with an acid solution containing a proportion of an acid soluble thorium compound substantially equivalent in amount to the ammonium fluoride content of the tungsten solution, recovering the precipitated tungstic acid and thorium fluoride admixture, and efi'ecting'the reduction of the tungsten component of the admixture to metal by heating the admixture to elevated temperatures in hydrogen.

In testimony whereof, I have hereunto sub- 3. The method of preparing thoriated ios scribed my name this 24th-day of July, 1926.

JOHN IHUMPHREYS RAMAGE. 

